Classically understood in video gaming context, the terms "RTS" and "4X" are pretty much mutually exclusive, even though some 4X titles are real-time, as you've noted.
That wasn't my understanding, and Wikipedia disagrees with you:
> 4X (abbreviation of Explore, Expand, Exploit, Exterminate) is a subgenre of strategy-based computer and board games, and include both turn-based and real-time strategy titles.
> 4X (abbreviation of Explore, Expand, Exploit, Exterminate) is a subgenre of strategy-based computer and board games, and include both turn-based and real-time strategy titles.